Magnetostrictive compressional wave transmitter or receiver



March 9, 1948. R. PEEK, m 2,437,270 v MAGNETOSTRICTIVE COMPRESSiONALWAVE TRANSMITTER OR REGEiVER,

Filed Nov. s, 1943 INVENTOR, y R.L.PEEK,JR. a

04am $1M A 7 TQRNE V sitely.

I Patented Mar. 9, 1948 MAGNE'IOSTBICTIVE COMPRESSION WAVE TRANSMITTEROR RECEIVER Robert L. Peek, Jr., Short Hills, N. 1.,ia1gm a5 BellTelephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Appllcation November 5, 1943,Serial No. 509,085

This invention relates to magnetostrictive devices and more particularlyto supersonic submarine signal translating devices of themagnetostrietive type;

Magnetostrictive devices comprise, in general,

a core of magnetostrictive material, a signal coil electromagneticallycoupled to the core and means for polarizing the core to establish inthe eifective parts thereof a biasing flux conducive to the realizationof large magnetostrictive action. The over-all magnetic emciency of suchdevices is dependent upon a number of factors principal among which arethe reluctance of the core to the flow of alternating flux therein andthe energy required to establish the requisite direct current biasingflux in the effective parts of the core. It has been proposed,heretofore, to obtain a low reluctance for the alternating fluxpath byconstructing the core so that in itself it defines a closed series pathfor the alternating flux. and to bias .the core by a permanent magnetseparate from the core. In one proposed construction, the core was inthe form of a rectangular loop and one pair of parallel legs thereof wasbiased in the same direction.

In submarine signaling devices wherein the magnetostrictive corecomprises parallel legs, simplicity of construction and mode ofoperation dictates that the parallel legs operate cophasally, that is,that the legsexpand and contract in the same direction in response to asignal flux impressed upon. the core or that the effect of the legs'whenactuated in response-to signal waves be cumulative. ,Hence, if the corebe in the form of a rectanguluar loop, it is necessary that the paralleloperative legs thereof-be polarized oppo- In such event, diiiicultiesare encountered due to, the possibility of magnetic saturation of otherparts of the core with consequent substantial increase of the totalreluctance of the path for the alternating flux. If such parts aremadeof sufilcient cross-section to avoid saturation thereof when thepolarizing flux in the parallel legs is of the requisite density. thecapacity of the polarizing magnet must be large, so that the magneticefllciency. of the device is reduced.

One object of this invention is to improve the construction andefliciency of magnetostrictive devices of the type having a coredefining a series magnetic circuit for alternating flux. More spe- '8Claims. (01. 117-386) section which provides a high reluctance for the Atransverse arm of the core.

2 tions or legs of which elongate and contract in the same direction inaccordance with signal fluxes impressed upon the core or compressionalwaves efiective upon the core. I

In one illustrative embodiment of the invention, a supersonic signalingdevice comprises a laminated rectangular core of magnetostrictivematerial, the core being mounted to be freely vibratile in the directionparallel to one pair of parallel legs thereof, a signal coil coupled tothe core and means for polarizing the core such that magnetostrictiveeiIects of like sign are produced in the pair of legs noted. In'onespecific construction, the polarizing flux is produced by 'a permanentmagnet having its poles opposite one end of the core so that the coredefines two paths, magnetically in parallel, one of the paths beingcomposed of the pair of legs noted and one of the transverse portions orarms of the core and the other path being composed of the other I Thelatter arm is provided with a short portion of restricted crossdirectcurrent polarizing flux traversing this arm: Thus, a high fluxdensity isobtained in the pair of arallel legs noted without saturation of thesecond path for the direct current flux. The efiect of the portion ofrestricted cross-section upon the direct currentflux in the arm in whichit is included is large. However, the effect of this portion upon thealternating flux, the path for which is serially around the core, isrelatively small because of the short length of this portion and due to.the inherent diflerence in the alternating current and direct currentpermeabilities thereof. Thus, a magnetically emcient core providing alow reluctance path for the signal flux and. wherein the requisite fluxdensity in the oscillatory legs is obtainable with a. relatively smallmagnet is realized.

The invention and the various features thereof will be understood moreclearly and fully from the following detailed description with referencetothe accompanying drawing, in which:

Fig. 1 is a perspectiveview oi. a submarine sig- 7 nalingdeviceillustrative of one embodiment of cifically, one object of thisinvention is to improve rectangular magnetostrictive corev which ispolarized by apermanent magnetand parallel porthis invention, portionsof the device being broken away to show details of construction moreclearly;

Fig. 2 is a detail view of the core and parts of the polarizing magnetincluded in the device shown in Fig. 1, illustrating typical paths forthe direct current and signal fluxes; and I Figs. 3 and 4 are diagramsillustrating core constructions illustrative of other embodiments ofthis invention.

assmvo netic material, for example brass or aluminum,

and having a raised portion II. The foundation member ID is seated uponand secured to a ring l2, also of non-magnetic material, which in turnis suitably secured to a wall l3 of a casing in which the device ismounted. Carried by the foundation member is a body ll of a materialcapable of efllciently transmitting supersonic compressional waveenergy. In a particularly advantageous construction, this body is of asoft rubber free of air cells therein and having substantially the samedensity and impedance for the transmission of compressional wave energyas sea water. The body it is provided with an annular flange l which issecured against a seating surface upon the support Ill by a clampingring i 6.

A 'magnetostrictive core, designated as a whole as H, bears against thebody II and is spaced from a flange I 8 on the support I 0 by aresilient gasket i9. Mounted on the raised portion H of the support inis a permanent magnet 20, of generally horseshoe form, having its polesoposite one end of the magnetostrictive core II. The magnet is securedin position by a non-magnetic clamping bar 2| which bears against re-'silient spacers or pads 22 and is aillxed to the support by screws 23; Acover 2|, seated upon the support I0, is held in placeby screws '25,only one ofwhich is shown, passing through resilient spacers or pads 26and threaded into the clamping bar 2|. A signal coil 2'! encompasses oneof the legs oi'the core I I and is supported from the flange It, theinternal dimensions of the coil being such as to provide clearancebetween th coil and core so that the coil will not impede motion of thecore.

The core I] is of generallyrectangular form and is formed of a pluralityof laminae of magnetostrictivematerial such as, for example, an alloycomprising of the order of 45 per cent nickel and balance principallyiron. the several laminae being secured together as by a suitablecement. The laminae may be provided with apertures 22 into which thecement flows. Specifically, each lamination ofthe core comprises a base29 in" intimate engagement with the body ll, 0. pair of parallel legs30a and 30b and a transverse-arm 3|. Advantageously, the body l4 andthe-core II are constructed and arranged to constitute a half-wavelengthresonator having a vibrational node adjacent the portion of the leg 30aencompassed by the signal coil 21, the frequency of resonance being thatat which the device is in.- tended to operate, if single frequencyoperation is desired, or the mean frequencyflf the device is intendedfor band frequency operation.

As illustrated clearly in Fig. 2, the poles of the magnet 20 areopposite the ends of the transverse arm SI of the core so that, for themagnet polarity indicated in Fig. 2, the direct current polarizing fluxflows in the directions indicated by the solid arrows, one path for thisflux being through the arm 3| and the other path being through the leg30a, base 29 and leg 30b in se-' rles. when a signal current is suppliedto the coil 21 or compressional waves are transmitted to the corethrough the body M, an alternating component of flux is superimposedupon the direct current flux, the flow of the signal flux componentbeing around the core, i. e., through the leg 30a, base 29, leg 30b andam It in seri s,

'4, as indicated by the dotted arrows in Fig. 2. It will be appreciated.then, that the core provides a closed magnetic path of low reluctancefor the alternating flux component so that an eillcient magnet circuitis realized, Inasmuch as the sign oi the flux change in the two legs 30aand 30b,

due to the signalflux, isthe same for both legs, it will be seen thatthe two legs will expand and contract in unison and thus transfer energycophasically to the body H through which the s18- nals are transmittedto the sea water. Conversely. the effect of the two less 30 in responseto compressional wave signals incident upon the body It will becumulative around the core.-

As is known,-optimum magnetostrictive effect is realized when themagnetostrictive core is polarized to a prescribed point, or, stated inanother way, optimum operation requires that the flux density in thelegs a and 30b be of prescribed value. The realization of this fluxdensity requires a magnet of a strength dependent upon the reluctance ofthe direct current path through the arm 3|. It will be apparent that ifthis reluctance is small, the total flux required to be supplied by themagnet 20 in order to produce the optium flux density in the legs 30will be large.

On the other hand, if this arm is made of small cross-section throughoutto increase its reluctance, this am may become saturated when thedesired flux density is produced in the legs 30 and, consequently, thereluctance of the path for the alternating flux would be large.

In accordance with a feature of this invention, the arm ii is soconstructed that the reluctance thereof to the now of direct currentflux is high while its reluctance to alternating flux is relatively lowwhereby the flux density in the legs 30 requisite for optimummagnetostrictive action can be obtained by use 01 a relatively smallmagnet. Specifically, as illustrated in Figs. 1 and 2, each laminationof the core is provided with a narrow slot or opening 82 in andextending transversely of the arm ii. The slots or apertures 32, it willbe noted, produce a localized reduction inthe cross-section of materialin the arm 3|, advantageously to less than the cross-section of each ofthe legs 30. Hence, the total direct current reluctance oi the pathdefined by the arm 3| is high and the requisite flux density in the legs30 can be obtained without saturation of the arm II and, as will beapparent, by the use of a relatively small magnet. In general, as isknown, the direct current permeability of a magnetic material is largein comparison to the alternating current permeability. Hence, the shortgap of substantial cross-sectional area defined by the slots orapertures 32 has a large eilect upon the directthe constructionillustration in Fig. 3. each lamination of the core is provided with aconstriction I32 whereby the direct current reluctance of the arm 3| issubstantially increased with only minor eflect upon the total reluctanceof the path for the signal flux, In Fig. 4, the increase in direct-current reluctance of the arm II is obtained by providing a shortair-gap 232 in the path defined by this arm. In both the constructionsillustrated in Figs, 3 and 4, the direct current polarizing flux may beobtained from a bar magnet I20 within the core, adjacent the arm 3| andhaving its poles adjacent the ends of this arm. Alternatively, ofcourse, a horseshoe form magnet, as shown in Fig. 1, may be employed inplace of the bar magnet in the constructions illustrated in Figs. 3 andAlthough specific embodiments of this invention have been shown anddescribed, it will be,

understood that they are but illustrative and that various modificationsmay be made therein without departing from the scope and spirit of thisinvention as defined in the appended claims.

What is claimed is:

1. A magnetostrictive device comprising a core defining a magnetic 100pand having therein a portion of greater reluctance than the remainder ofthe loop and a magnetostrictive portion separate from said firstportion, a signal coil electromagnetically coupled to said loop, meansmount ing said core for substantially free vibration, and a permanentmagnet having its poles opposite the ends of said first portion.

2. A signaling device comprising a core including parallelmagnetostrictive legs and portions defining a series magnetic circuitwith said legs, one of said portions having a section of high directcurrent reluctance, a permanent magnet having its poles opposite theends of said one portion and remote from the other of said portions, andmeans for driving said legs longitudinally and in the same direction. v

3. A magnetostrictive device comprising a closed magnetic circuit, meansfor polarizing said circuit, said circuit being defined by two branchesmagnetically in parallel with respect to the direction of flow of thepolarizing flux therethrough, one of said branches including a linearportion of m'agnetostrictive material and the other of said brancheshaving a restricted section of high direct current reluctance, and meansfor actuating said linear portion in the direction of its length.

4. A signal translating device comprising a core including a U-shapedportion of magnetostrictive material and an arm bridged across the endsof said portion; means mounting said core for oscillation thereofparallel to the arms of said U- shaped portion, means for polarizingsaid U- shaped portion and said arm magnetically in Parallel and asignal coil coupled to said U-shaped portion, said arm having therein arestricted section of high reluctance.

5. A signal translating device comprising a magnetostrictive core havinga pair of parallel legs and arms bridging said legs, means mounting saidcore for vibration parallel to said legs, one of said arms having arestricted portion of reduced cross-section, a signal coil coupled tosaid core, and a permanent magnet having its poles opposite the ends ofsaid one arm. 6. A signal translating device comprising a substantiallyrectangular magnetostrictive core, means mounting said core forvibration parallel to one pair of opposite sides thereof, a signal coilcoupled to said core, one of the other sides of said core having thereina restricted slot extending transversely thereof, and a permanent magnethaving its poles opposite the ends of said one other side.

7. A signal translating device comprising a core of magnetostrictivematerial including a pair of parallel legs and a pair of arms bridgingsaid legs and defining a closed magnetic loop therewith, a signal coilcoupled to said core, means mounting said core for oscillation parallelto said legs, and a permanent magnet having its poles opposite the endsof one of said arms, said one arm having a restricted portion of reducedcrosssection,

8. A signal translating device comprising a laminated magnetostrictivecore including a base portion. a pair of parallel legs extending fromsaid base portionand an arm bridging said legs, means mounting said corefor vibration parallel to said legs, a compressional wave signaltransmitting body in engagement with said base portion, a signal coilcoupled to said core, said arm having therein a restricted portion ofreduced cross-section, and means for establishing a polarizing flux insaid core traversing two paths in parallel, one of said paths includingsaid restricted portion and the other of said paths comprising said legsand said base portion in series.

ROBERT L. PEEK, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITE STATES PATENTS

